EP3406780B1 - Annealed meltblown nonwoven fabric with high compression hardness - Google Patents

Description

The present invention relates to a tempered meltblown nonwoven with a high compression hardness and in particular to a tempered voluminous meltblown nonwoven with a high compression hardness. Furthermore, the present invention relates to a method for producing such a tempered meltblown nonwoven.

Felts and nonwovens are usually produced from staple fibers and / or continuous filaments by means of known mechanical or aerodynamic processes. A well-known aerodynamic process is the meltblown process based on the Exxon principle, such as that in the US 3,755,527 is described. In this process, a low-viscosity polymer is extruded through capillaries located at the tip of a nozzle. The polymer droplets that form are then subjected to an air flow, which is referred to as blown air and has a high temperature and speed, from two sides, as a result of which the polymer droplets are drawn out into a polymer free jet in the form of fine filaments. As a result of the air currents hitting the polymer drops at an acute angle, an oscillation process is also induced in the polymer free jet in the then available free jet, as a result of which high-frequency processes occur which accelerate the polymer strands beyond the speed of the blown air. As a result, the polymer strands are additionally stretched, so that the filaments obtained after the filaments have been deposited on a support and after cooling can have a diameter and fineness in the single-digit micrometer range or even less. The meltblown nonwovens or meltblown nonwovens produced in this way are used for various applications, for example for barrier functions in the hygiene area. For these applications, the filaments are placed on the carrier as a flat, two-dimensional nonwoven.

Another known meltblown process is from Biax Fiberfilm Corp. developed and for example in the US 4,380,570 have been described.

Voluminous, three-dimensional meltblown nonwovens can also be produced by depositing the filaments formed between two suction drums or double drums, as is the case, for example, in DE 17 85 712 C3 and in the US 4,375,446 is described. These voluminous meltblown nonwovens can be used, for example, as oil absorbers or as acoustic damping materials. However, these voluminous meltblown nonwovens have the disadvantage that they are very ductile and are characterized by poor relaxation, which leads to a loss of volume after pressure load.

From the US 4,118,531 Meltblown nonwovens are known which contain, in addition to the meltblown filaments, staple fibers of polyethylene terephthalate incorporated therein. These nonwovens are characterized by increased resilience, which is why the nonwoven has better relaxation. However, these nonwovens are constructed from two incompatible polymers, which precludes recycling, which in turn leads to a major cost disadvantage.

A major disadvantage of the known meltblown nonwovens and in particular of the known voluminous meltblown nonwovens is their comparatively low rigidity and the resulting low compression hardness, in particular under higher loads. Furthermore, these materials are usually limp, which means that they deform under their own weight, but not a specific one Keep in shape. For these reasons, these known meltblown nonwovens and in particular known voluminous meltblown nonwovens are difficult to convert permanently into a predetermined shape. Deformation generally leads to compression of these nonwovens.

It is therefore an object of the present invention to provide a meltblown nonwoven, and in particular a voluminous meltblown nonwoven, which has increased rigidity and, in particular, an increased compression hardness, especially under greater loads, and which is also easy to convert into a predetermined, permanent shape.

According to the invention, this object is achieved by a tempered meltblown nonwoven fabric which can be obtained by a process in which at least some of the meltblown nonwoven fabric is subsequently tempered at a temperature which is between the glass transition temperature and 0.1 ° C. below the melting temperature of the filaments of the meltblown nonwoven, the meltblown nonwoven being composed of filaments from a polyolefin, and the meltblown nonwoven having a basis weight of 100 to 600 g / m ² , a density of 5 to 50 kg / m ³ and one in accordance with DIN EN Compression hardness measured according to ISO 3386 at 60% compression of at least 2 kPa.

This solution is based on the surprising finding that a voluminous meltblown nonwoven which is subsequently tempered at a temperature between the glass transition temperature and 0.1 ° C below the melting temperature of the filaments of the meltblown nonwoven, namely one with a basis weight of 100 to 600 g / m ² and with a density of 5 to 50 kg / m ³ , has a significantly increased stiffness compared to the corresponding unannealed meltblown nonwoven. Because of this, the meltblown nonwoven fabric according to the invention is also characterized by a significantly increased compression hardness, especially under greater loads, such as, for example, at 40% or 60% compression , namely by a compression hardness measured according to DIN EN ISO 3386 at 60% compression of at least 2 kPa. Furthermore, the meltblown nonwoven according to the invention can easily be shaped into a desired shape during the tempering. Without wishing to be bound by theory, it is assumed that these advantages are at least partly due to the fact that the degree of crystallization of the nonwoven filaments, which were previously predominantly amorphous, is significantly increased during the subsequent annealing carried out according to the invention. This is suspected because the inventors found that the melting temperature of the filaments of the meltblown nonwoven fabric can increase by about 10 to 20 ° C depending on the conditions during the annealing. The experiments carried out by the inventors seem to show that the very high take-off speeds in the production of the filaments to very thin finenesses of the filaments, despite the hot blown air, leads to a rapid cooling of the polymer melt, so to speak that the amorphous molecular structure of the melt "freezes"" becomes. As explained, the degree of crystallization of the amorphous nonwoven filaments is increased by the annealing according to the invention. Advantageously, the filament fineness and the nonwoven structure are not changed, or at most only insignificantly, by the tempering, so that after the tempering the nonwoven maintains its other properties, such as, for example, in the case of a voluminous nonwoven, its thickness-specific acoustic properties, such as the degree of acoustic absorption.

For the purposes of the present invention, a meltblown nonwoven is understood to mean a nonwoven fabric produced using one of the known meltblown processes, regardless of whether it is a two-dimensional nonwoven or a voluminous nonwoven. Processes for producing such meltblown nonwovens are, for example, in US Pat US 4,118,531 , in the US 4,375,446 , in the US 4,380,570 and in the DE 17 85 712 C3 described.

In addition, in the sense of the present invention, annealing is generally understood to mean a heat treatment, that is to say the heating of the meltblown nonwoven at the aforementioned temperature for a certain period of time.

According to the invention, at least part of the meltblown nonwoven is subsequently annealed, specifically at a temperature which is between the glass transition temperature and 0.1 ° C. below the melting temperature of the filaments of the meltblown nonwoven. Both the glass transition temperature and the melting temperature of the filaments of the meltblown nonwoven refer to the corresponding temperatures of the meltblown nonwoven present at the time. As stated above, the inventors have found that the melting temperature of the filaments of the meltblown nonwoven fabric can increase by about 10 to 20 ° C depending on the conditions during the annealing. Therefore, the temperature can be raised during annealing. For example, if the melting temperature of the filaments of the meltblown nonwoven is 152 ° C. before the beginning of the tempering and the melting temperature of the filaments of the meltblown nonwoven increases during tempering, for example to 170 ° C., the tempering can be carried out, for example, in such a way that the meltblown nonwoven is first annealed at a temperature of 150 ° C, after a certain period of time, for example 10 minutes, the temperature is increased to 155 ° C (which is 2 ° C below the melting temperature which the filaments of the meltblown nonwoven have at this time), before after a further period of 10 minutes, for example, the temperature is raised again to 165 ° C. (which is 2 ° C. below the melting temperature which the filaments of the meltblown nonwoven have at this point in time).

The meltblown nonwoven is partially or fully annealed. In this case, a specific partial area of the meltblown nonwoven or several partial areas of the meltblown nonwoven can be annealed, whereas the rest of the meltblown nonwoven remains untempered. It is also possible and, according to the present invention, particularly preferred to heat the entire meltblown nonwoven.

Good results both with regard to the formability and with regard to the increase in the rigidity and in particular the compression hardness of the tempered meltblown nonwoven are obtained in particular if the meltblown nonwoven or the subarea (s) to be tempered at one temperature is / are annealed, which is between 20 ° C below the melting temperature and 1 ° C below the melting temperature of the filaments of the meltblown nonwoven. The tempering is particularly preferably carried out at a temperature which is between 15 ° C. below the melting temperature and 1 ° C. below the melting temperature and very particularly preferably between 10 ° C. below the melting temperature and 2 ° C. below the melting temperature, for example at about 5 ° C below the melting temperature (for example between 8 ° C below the melting temperature and 2 ° C below the melting temperature) of the filaments of the meltblown nonwoven.

The duration of the annealing depends on the temperature to which the meltblown nonwoven is heated during the annealing, with a lower annealing temperature tending to require a longer annealing period. Basically, an annealing period of 1 minute to 10 days and in particular 2 minutes to 24 hours has proven to be suitable. The period of annealing is preferably 2 minutes to 2 hours, particularly preferably 2 to 60 minutes and most preferably 2 to 10 minutes.

Good results are achieved in particular if the meltblown nonwoven is annealed for 2 minutes to 2 hours at a temperature which is between 20 ° C. below the melting temperature and 1 ° C. below the melting temperature of the filaments of the meltblown nonwoven. Annealing is particularly preferred of the meltblown nonwoven is carried out for 2 to 60 minutes at a temperature which is between 15 ° C. below the melting temperature and 2 ° C. below the melting temperature of the filaments of the meltblown nonwoven, and the tempering of the meltblown nonwoven is very particularly preferred for 2 to 10 minutes at a temperature which is about 5 ° C below the melting temperature, that is between 8 ° C below the melting temperature and 2 ° C below the melting temperature of the filaments of the meltblown nonwoven.

As stated above, the melting point of the meltblown nonwoven may increase during annealing due to the increase in the degree of crystallization. In this case, at a constant tempering temperature, the distance between the tempering temperature and the melting point of the meltblown nonwoven would increase more and more during the tempering, and the required tempering time would be comparatively long. Therefore, in accordance with an alternative embodiment of the present invention, it is proposed to increase the temperature during the annealing in order to keep the annealing temperature always just below (for example about 2 ° C. or 5 ° C.) below the melting point of the meltblown nonwoven which increases during the annealing , For example, if the melting temperature of the filaments of the meltblown nonwoven is 152 ° C. before the beginning of the tempering and the melting temperature of the filaments of the meltblown nonwoven increases to 170 ° C. during the tempering, for example, the tempering can be carried out as described above, for example that the meltblown nonwoven is first tempered at a temperature of 150 ° C, after a certain period of time, for example 10 minutes, the temperature is 155 ° C (which is 2 ° C below the melting temperature that the filaments of the meltblown nonwoven at this time ) is increased before, after a further period of 10 minutes, for example, the temperature is again increased to 165 ° C. (which is 2 ° C. below the melting temperature that the filaments of the meltblown nonwoven have at this point in time).

In principle, the present invention is not restricted with regard to the way in which the meltblown nonwoven is annealed. Annealing, in which hot melt and / or superheated steam is applied to the meltblown nonwoven fabric, has proven to be not only simple, but particularly effective. In this embodiment, the hot air or the superheated water vapor has a temperature which corresponds to that to which the meltblown nonwoven is to be heated during the annealing. In this embodiment, hot air or superheated steam is preferably applied to the meltblown nonwoven by flowing hot air or superheated steam around the meltblown nonwoven or, more preferably, flowing through it.

In order to achieve this, the meltblown nonwoven is preferably annealed in an oven which has at least one blow box which is arranged such that the hot air or the superheated steam can be blown into the meltblown nonwoven. If only one or more areas of the meltblown nonwoven are to be tempered, the blow box should be designed so that the hot air or the superheated steam is only blown into the area (s) of the meltblown nonwoven to be tempered.

In a further development of the inventive concept, it is proposed that the meltblown nonwoven be annealed in an oven which has at least one suction box, which is arranged such that air flowing through the meltblown nonwoven or superheated water vapor can be sucked off in order to ensure a safe flow guarantee. Vacuuming on both sides ensures that hot air or superheated water vapor flows safely through the nonwoven fabric and that the nonwoven fabric does not collapse but maintains its volume.

According to a particularly preferred embodiment of the present invention, the meltblown nonwoven is annealed in an oven which has at least one blow box and at least one suction box, the at least one blow box being arranged such that the hot air or the superheated water vapor in the meltblown Nonwoven can be blown in, and, wherein the at least one suction box is arranged so that the air flowing through the meltblown nonwoven or superheated water vapor can be sucked off. In this embodiment, the furnace particularly preferably has two blow boxes and one or two suction boxes, the suction box being arranged downstream of the first or second blowing box in the case of a suction box, and, the two suction boxes being downstream of the first and the second in the case of two suction boxes Blow box are arranged.

According to the invention, the meltblown nonwoven has a weight per unit area of 100 to 600 g / m ² , preferably 100 to 400 g / m ² and particularly preferably 250 to 350 g / m ² , such as 350 g / m ² .

The meltblown nonwoven is preferably a voluminous meltblown nonwoven with a density of 8 to 25 kg / m ³ and particularly preferably of 10 to 20 kg / m ³ .

Preferably, the filaments of the meltblown nonwoven according to the present invention are composed of a polymer selected from the group consisting of polypropylene and polyethylene. The filaments of the meltblown nonwoven according to the present invention are very particularly preferably composed of isotactic polypropylene, since it has been found that the degree of crystallization is particularly well increased during the tempering in filaments made of isotactic polypropylene.

For materials that do not show particularly good crystallization behavior, this can be increased by adding crystallization nuclei during the extrusion process.

In a further development of the inventive concept, it is proposed to anneal the meltblown nonwoven in a shaped body in order to also convert the meltblown nonwoven into a predetermined shape during the annealing. This can be achieved, for example, in that the molded body in which the meltblown nonwoven is tempered is at least partially designed as a sieve, so that the meltblown nonwoven is flowed through and / or flowed around with hot air or with superheated steam during the tempering can.

In an alternative embodiment, it is proposed to place the meltblown nonwoven after heating, but before cooling, in a shaped body and thus to convert it into a predetermined shape in order to shape it, the meltblown nonwoven being cooled in the mold in order to complete the tempering process ,

In this way, for example, the meltblown nonwoven can be shaped into a specific shape, such as a hemisphere, by tempering as a stamped part. The meltblown nonwoven fabric, tempered and shaped in this way, is significantly more dimensionally stable than the starting material and largely retains its shape. The meltblown nonwoven can therefore take on forces after tempering, so that additional stiffening structural elements in the meltblown nonwoven can be dispensed with after molding.

According to a further preferred embodiment of the present invention, it is provided that at least one spacer, which has a length that is greater than the thickness of the meltblown nonwoven, is provided in the meltblown nonwoven and is arranged in the thickness direction of the meltblown nonwoven. This is advantageous, for example, if the meltblown nonwoven is to be used as an acoustic absorber. By molding the spacer (s) in the rigid meltblown nonwoven fabric, an inherently rigid molded part is obtained, in which, due to the spacer (s) - if it acts as an acoustic absorber in front of a reflective plane, such as the sheet metal wall of an automobile, is mounted - a not insignificant air gap is formed between the absorber and the reflecting plane, the additional air volume thus created acting as an integral part of the absorber structure. As a result, a molded part made of meltblown nonwoven fabric with an excellent absorber effect can be achieved with a significantly reduced material expenditure. The air volume enclosed between the absorber and the wall results in a significant improvement in the low-frequency behavior of the structure, which can otherwise only be achieved by means of correspondingly thick and thus also heavy and expensive materials. In a further embodiment according to the invention, the air volume between the absorber and the wall described above can also be created by a structure of the wall with a flat absorber or a structure of the wall and the absorber, the inherent rigidity of the absorber being necessary for the permanent formation of the air volume.

As stated, the meltblown nonwoven to be tempered can be made by any of the known meltblown processes, such as one in the art US 4,118,531 , in the US 4,375,446 , in the US 4,380,570 or in the DE 17 85 712 C3 described method. In principle, a meltblown process is used to produce nonwoven by extruding polymer melt extruded through a nozzle on the outside with flowing air and stretching it before the filaments thus formed are placed on a carrier and cooled. The carrier is preferably a double suction drum.

As shown, the degree of crystallization of the meltblown nonwoven is increased by the annealing. The filaments of the annealed meltblown nonwoven preferably have at least in sections and preferably over the entire surface, a degree of crystallization of 20 to 80%, more preferably 30 to 75%, particularly preferably 40 to 75% and most preferably 50 to 70%. If the meltblown nonwoven is annealed only in sections, the tempered areas of the annealed meltblown nonwoven preferably have a degree of crystallization of 20 to 80%, more preferably 30 to 75%, particularly preferably 40 to 75% and most preferably 50 to 70 % on.

According to the invention, the meltblown nonwoven has, at least in sections and preferably over the entire surface, a compression hardness (compressive stress) measured at 60% compression of at least 2 kPa based on DIN EN ISO 3386. The meltblown nonwoven preferably has, at least in sections and preferably over the entire area, a compression hardness (compressive stress) measured in accordance with DIN EN ISO 3386 at 60% compression of at least 8 kPa, particularly preferably of at least 12 kPa, very particularly preferably of at least 20 kPa and maximum preferably has at least 30 kPa. Contrary to the above-mentioned standard, the compression hardness at 60% compression is to be understood as the compressive stress under which a material sample is reduced by 60% of the original thickness. Furthermore, the preload for determining the initial thickness of the material is reduced to 0.014 kPa in order to take into account the very low compression hardness of the untempered material. In the case of deviating degrees of compression or other test conditions, deviating compressive stresses with non-linear relationships to the stated values can result.

In order to shorten the annealing time, it is proposed in a further development of the inventive concept to raise the annealing temperature continuously or in stages during the annealing, and preferably also above the melting temperature of the non-annealed filaments of the meltblown nonwoven, the annealing temperature, however, always being at least 0.1 ° C below the current (ie the melting temperature of the filaments of the meltblown nonwoven at this time.

Overall, the present invention makes it possible to increase the degree of crystallization of the filaments of meltblown nonwovens in sections or over the entire area, and thus to increase the rigidity of meltblown nonwovens in sections or over the entire area. In particular, the present invention can be used to anneal the entire surface of the meltblown nonwoven and thus to increase the degree of crystallization in the entire area of the meltblown nonwoven. This enables the production of rigid, pressure-stable two-dimensional components. As an alternative to this, the shaped meltblown nonwoven can also only be partially annealed and the degree of crystallization in the meltblown nonwoven can only be raised over part of the surface, for example to increase the rigidity only in component-specific areas or in the continuous grid of the component. For example, only the edge areas of the component made of the meltblown nonwoven can be annealed in order to make the edge areas of the component more rigid, for example to increase the stackability of the component made of the meltblown nonwoven. As an alternative to this, tempering can be used to form a component from the meltblown nonwoven and to increase the degree of crystallization over the entire surface in order to produce inherently rigid three-dimensional components. On the other hand, it is also possible to deform the meltblown nonwoven only partially over the surface and to increase the degree of crystallization only in this partial surface, for example in order to thereby form one or more spacers or another local functional geometry in the meltblown nonwoven. In all of the aforementioned application options, locally condensed or consolidated areas can expand the functionality, for example for the formation of contact surfaces at fastening points.

Another object of the present invention is a tempered meltblown nonwoven whose filaments are at least in sections and preferably over the entire surface have a degree of crystallization of 20 to 80%, preferably 30 to 75%, particularly preferably 40 to 75% and most preferably 50 to 70%.

Furthermore, the present invention relates to a meltblown nonwoven with a compression hardness measured at least in sections and preferably over the entire surface in accordance with DIN EN ISO 3386 at 60% compression of at least 2 kPa. The meltblown nonwoven according to the invention preferably has a compression hardness at 60% compression of at least 8 kPa, particularly preferably of at least 12 kPa, very particularly preferably of at least 20 kPa and most preferably of at least 30 kPa.

1. a) Herstellen eines Meltblown-Vliesstoffs vorzugsweise indem durch eine Düse extrudierte Polyolefinpolymerschmelze außenseitig mit strömender Luft beaufschlagt und verstreckt wird, bevor die dadurch ausgebildeten Filamente auf einem Träger, welcher bevorzugt eine Doppel-Saugtrommel ist, abgelegt und abgekühlt werden, sowie
2. b) Tempern zumindest wenigstens eines Abschnittes des in dem Schritt a) hergestellten Meltblown-Vliesstoffs bei einer Temperatur, die zwischen der Glasübergangstemperatur und 0,1 °C unterhalb der Schmelztemperatur der Filamente des Meltblown-Vliesstoffs liegt.

Another object of the present invention is a method for producing a tempered meltblown nonwoven with a basis weight of 100 to 600 g / m ² and with a density of 5 to 50 kg / m ³ comprising the following steps:

1. a) Manufacture of a meltblown nonwoven, preferably by applying extruded polyolefin polymer melt on the outside with flowing air and stretching it before the filaments thus formed are placed and cooled on a support, which is preferably a double suction drum, and
2. b) tempering at least a portion of the meltblown nonwoven fabric produced in step a) at a temperature which is between the glass transition temperature and 0.1 ° C below the melting temperature of the filaments of the meltblown nonwoven fabric.

The process steps described as preferred above for the meltblown nonwoven according to the invention also apply to the process according to the invention.

Accordingly, it is particularly preferred that the meltblown nonwoven in step b) is annealed for 2 minutes to 2 hours at a temperature which is between 20 ° C. below the melting temperature and 1 ° C. below the melting temperature of the filaments of the meltblown nonwoven ,

The present invention is described below with reference to these illustrative, but not restrictive figures.

Fig. 1

schematisch einen Ofen zur Herstellung eines getemperten Meltblown-Vliesstoffs gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.

Fig. 2

schematisch eine Form zum gleichzeitigen Formen und Tempern eines Meltblown-Vliesstoffs gemäß einem anderen Ausführungsbeispiel der vorliegenden Erfindung.

Fig. 3

die Ergebnisse der Messung der Schallabsorption des in dem Beispiel 1 hergestellten getemperten Meltblown-Vliesstoffs gemäß der vorliegenden Erfindung (Kurve A) im Vergleich zu dem in dem Vergleichsbeispiel hergestellten ungetemperten Meltblown-Vliesstoff (Kurve B).

Fig. 4

die Ergebnisse der Messung des Absorptionskoeffizienten des in dem Beispiel 1 hergestellten getemperten Meltblown-Vliesstoffs direkt an eine Karosseriewand angebracht (Kurve A), in einem Abstand von 10 mm an eine Karosseriewand angebracht (Kurve B) und in einem Abstand von 40 mm an eine Karosseriewand angebracht (Kurve C).

Show:

Fig. 1

schematically an oven for producing a tempered meltblown nonwoven according to an embodiment of the present invention.

Fig. 2

schematically shows a mold for simultaneously molding and annealing a meltblown nonwoven according to another embodiment of the present invention.

Fig. 3

the results of the measurement of the sound absorption of the tempered meltblown nonwoven fabricated in Example 1 according to the present invention (curve A) in comparison with the untempered meltblown nonwoven fabric produced in the comparative example (curve B).

Fig. 4

the results of the measurement of the absorption coefficient of the tempered meltblown nonwoven fabric produced in Example 1 attached directly to a body wall (curve A), attached at a distance of 10 mm to a body wall (curve B) and at a distance of 40 mm to a body wall attached (curve C).

The Fig. 1 schematically shows a belt furnace 10 for producing a tempered meltblown nonwoven according to an embodiment of the present invention. The open 10 comprises air-permeable belts 14, 14 'which are guided and driven on rollers 12 and via which the meltblown nonwoven fabric 15 is guided into and through the oven 10. A first blow box 16, a suction box 18 and a second blow box 16 'are arranged in the furnace 10 above and below the two belts 14, 14', viewed in the conveying direction from right to left in this order. During operation of the furnace 10, the meltblown nonwoven 15 is passed through the furnace 10 from right to left on the lower belt 14. When passing through the blow boxes 16, 16 ', hot air is flowed into and through the meltblown nonwoven fabric 15 in order to raise the filaments of the meltblown nonwoven fabric 15 to the desired tempering temperature. In the area of the suction box 18, air flowing through the meltblown nonwoven 15 is sucked off to ensure that the meltblown nonwoven 15 is safely flowed through by the hot air and the meltblown nonwoven 15 does not collapse but maintains its volume.

In the Fig. 2 schematically shows a mold 20 for the simultaneous molding and tempering of a meltblown nonwoven fabric 15 according to another exemplary embodiment of the present invention. The meltblown nonwoven fabric 15 is held in the desired shape from both sides by appropriately shaped sieves 22, 22 ', from which the mold 20 is composed, and heated to the desired temperature by tempering or flowing hot air around it. The nonwoven mat produced in this way retains the embossed shape and is dimensionally stable.

The present invention is described below with reference to illustrative but not restrictive examples.

example 1

A meltblown nonwoven fabric with a basis weight of 300 g / m ² and a density of 15 kg / m ^{3 was} produced from filaments made of isotactic polypropylene with a filament fineness of 5 µm on average by using the US 4,375,446 described meltblown process was carried out. This meltblown nonwoven was then heat-treated in a forced air oven at 158 ° C. for 10 minutes. By inserting the cold nonwoven and opening the oven door, the initial temperature was below the melting point of the filaments of the unheated nonwoven. Due to the immediate onset of crystallization with an accompanying increase in the melting point of the filaments, the rest of the 10 minutes could be further tempered at 158 ° C, i.e. above the melting temperature of the unheated filaments, but below the melting temperature of the filaments present at the time, and so on Tempering time can be shortened compared to tempering at a lower temperature.

Thereafter, the compression hardness at 40% compression and the compression hardness at 60% compression of the tempered meltblown nonwoven was measured in accordance with DIN EN ISO 3386. The results are summarized in Table 1 below and show that the tempering according to the invention leads to a drastic increase in the compression hardness.

In addition, the degree of sound absorption of the tempered meltblown nonwoven was measured as a function of the thickness-standardized frequency in accordance with DIN EN ISO 10534. The results are in the Fig. 3 in curve A in comparison to the values which have been achieved with the unannealed meltblown nonwoven fabric produced in the comparative example (curve B). The unit of the abscissa is the measurement frequency x absorber thickness / 15 mm. The comparison of the results shows that the heat treatment according to the invention has no negative effects on the sound absorption properties of the nonwoven.

Part of the tempered meltblown nonwoven was attached directly to a motor vehicle body wall, whereas another part of the tempered meltblown nonwoven was attached to a motor vehicle body wall with a distance of 10 mm and another part of the tempered meltblown nonwoven with a spacing of 40 mm was attached to a car body wall. The absorption coefficient as a function of frequency was then determined for the three structures. The results are in the Fig. 4 shown, curve A shows the values for the meltblown non-woven fabric attached directly to the vehicle body wall, curve B shows the values for the meltblown non-woven fabric attached to the vehicle body wall with a distance of 10 mm, and curve C the Values for the meltblown nonwoven attached to the car body wall at a distance of 40 mm. A comparison of the values obtained shows that the air volume enclosed between the nonwoven fabric and the body wall results in a significant improvement, particularly in the low-frequency absorption properties of the bodywork, which can otherwise only be achieved by means of correspondingly thick and thus also heavy and expensive materials.

Example 2

An annealed meltblown nonwoven fabric was made according to the procedure described in Example 1, except that the annealing was carried out at 155 ° C for 10 minutes.

Example 3

An annealed meltblown nonwoven fabric was made according to the procedure described in Example 1, except that the annealing was carried out at 155 ° C for 25 minutes.

Comparative example

An untempered meltblown nonwoven fabric was produced in accordance with the first process step described in Example 1, which, unlike the one described in Example 1, was not annealed. Table 1 example Annealing temperature (° C) Annealing time (min.) Compression hardness factor at 60% compression Compression hardness factor at 60% compression 1 158 10 18.5 14 2 155 10 9.5 7 3 155 25 12 9 Comparative Example 1 - - 1 1 Compression hardness factor: Ratio of the compression hardness of the annealed nonwoven fabric of the example divided by the compression hardness of the non-annealed nonwoven fabric of the comparative example

A comparison of the results shows that the subsequent tempering of the meltblown nonwoven leads to a drastic increase in the compression hardness of the meltblown nonwoven.

LIST OF REFERENCE NUMBERS

10

oven (volume)

12

roll

14, 14 '

Breathable tape

15

Meltblown nonwoven

16, 16 '

blow box

18

suction box

20

shape

22, 22 '

scree

Claims (15)

1. An annealed meltblown nonwoven fabric, obtainable by means of a method in which at least a portion of the meltblown nonwoven fabric (15) is subsequently annealed at a temperature between the glass transition temperature and 0.1 °C below the current melting temperature of the filaments of the meltblown nonwoven fabric (15), the meltblown nonwoven fabric (15) being composed of filaments of a polyolefin, and the meltblown nonwoven fabric (15) having a weight per unit area of 100 to 600 g/m², a density of from 5 to 50 kg/m³, and a compression hardness at 60% compression of at least 2 kPa as measured according to DIN EN ISO 3386.
2. The meltblown nonwoven fabric as set forth in claim 1, characterized in that the meltblown nonwoven fabric (15) is tempered at a temperature between 20 °C and 1 °C below the current melting temperature of the filaments of the meltblown nonwoven fabric (15), preferably between 15 °C and 1 °C below the current melting temperature of the filaments of the meltblown nonwoven fabric (15), and more preferably between 10 °C and 2 °C below the actual melting temperature of the filaments of the meltblown nonwoven fabric (15).
3. The meltblown nonwoven fabric as set forth in claim 1 or 2, characterized in that the meltblown nonwoven fabric (15) is annealed at the temperature for 1 minute to 10 days, preferably for 2 minutes to 24 hours, especially preferably for 2 minutes to 2 hours, very especially preferably for 2 to 60 minutes, and most preferably for 2 to 10 minutes.
4. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the meltblown nonwoven fabric (15) is annealed through exposure to hot air and/or superheated steam.
5. The meltblown nonwoven fabric as set forth in claim 4, characterized in that the meltblown nonwoven fabric (15) is annealed in a furnace (10) having at least one blast box (16, 16') and at least one suction box (18), preferably two blast boxes (16, 16') and at least two suction boxes (18), the at least one blast box (16, 16') being arranged such that the hot air can be blown into the meltblown nonwoven fabric (15), and the at least one suction box (18) being arranged such that air flowing through the meltblown nonwoven fabric (15) can be extracted.
6. The meltblown nonwoven fabric as set forth in claim 4, characterized in that the meltblown nonwoven fabric (15) has a weight per unit area of from 100 to 400 g/m² and especially preferably from 250 to 350 g/m².
7. The meltblown nonwoven fabric as set forth in claim 4, characterized in that the meltblown nonwoven fabric (15) is a voluminous meltblown nonwoven fabric (15) having a density of from 8 to 25 kg/m³ and especially preferably from 10 to 20 kg/m³.
8. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the meltblown nonwoven fabric (15) is composed of filaments that are made of polypropylene and/or polyethylene.
9. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that

   i) the meltblown nonwoven fabric (15) is annealed in a mold (20) for the purpose of reshaping it during annealing, the mold (20) being preferably embodied at least partially as a screen (22, 22'), so that the meltblown nonwoven fabric (15) can be flowed through and/or flowed around with hot air and/or with superheated steam during tempering, and/or

   ii) the meltblown nonwoven fabric (15) is transferred to a mold (20) after heating for the purpose of reshaping it, in which case the meltblown nonwoven fabric (15) is cooled in the mold in order to conclude the annealing process.
10. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that at least one spacer is provided in the meltblown nonwoven fabric (15) that is arranged in the direction of thickness of the meltblown nonwoven fabric (15) and, as a result of permanent molding, has a length that is greater than the length of the meltblown nonwoven fabric (15).
11. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the meltblown nonwoven fabric (15) that is subsequently annealed was manufactured by applying flowing air to the outside of a polymer melt that is extruded through a die and drawing said polymer melt before the filaments that are formed in this way are placed onto a carrier, which is preferably a dual suction drum, and cooled.
12. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the filaments of the meltblown nonwoven fabric (15) have a degree of crystallinity of from 20 to 80%, preferably from 30 to 75%, especially preferably from 40 to 75%, and most preferably from 50 to 70%.
13. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the meltblown nonwoven fabric (15) has a compression hardness at 60% compression of at least 8 kPa, especially preferably of at least 12 kPa, very especially preferably of at least 20 kPa, and most preferably of at least 30 kPa as measured according to DIN EN ISO 3386.
14. The meltblown nonwoven fabric as set forth in at least one of the preceding claims, characterized in that the annealing temperature is increased in a continuous or stepwise manner during annealing, preferably even beyond the melting temperature of the non-annealed filaments of the meltblown nonwoven fabric, but on the proviso that the annealing temperature be always at least 0.1 °C below the current melting temperature of the filaments of the meltblown nonwoven fabric existing at this point in time.
15. A method for manufacturing an annealed meltblown nonwoven fabric having a weight per unit area of from 100 to 600 g/m² and having a density of from 5 to 50 kg/m³, comprising the following steps:

    a) manufacturing a meltblown nonwoven fabric (15), preferably by applying flowing air to the outside of a polymer melt that is extruded through a die and drawing said polymer melt before the filaments that are formed in this way are placed onto a carrier, which is preferably a dual suction drum, and cooled, and

    b) annealing at least a portion of the meltblown nonwoven fabric prepared in step a) at a temperature between the glass transition temperature and 0.1 °C below the melting temperature of the filaments of the meltblown nonwoven fabric.

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